The goal of our work is to elucidate the mechanisms that are involved in the initiation and progression of liver regeneration following partial hepatectomy in rats. The existence of a lag phase of about 16 hours between partial hepatectomy and the start of DNA synthesis indicates that metabolic changes essential for DNA replication take place during this time. We suggest that polyamines and amino acids play an important role in the sequence of metabolic events that culminate in cell division. This proposal involves a number of projects which are the components of a research effort designed to elucidate a) the mechanisms that regulate polyamine synthesis during liver regeneration and the relationships between polyamine and RNA metabolism; b) the role of amino acids in the initiation and progression of the regenerative response; c) the role of m-RNA synthesis and transport in programming liver cells to replicate. This study should provide a more precise understanding of the regulation of normal and cancerous growth in the mammalian liver.